The class of thermoplastic polymers is well known in the art, being particularly useful because of the property exhibited by many of the polymers of being deformable at relatively low temperatures. Thus, such thermoplastics are processed by conventional techniques such as extrusion, injection molding or thermoforming into sheets, films, fibers, molded articles and other useful objects without undue degradation of the polymer.
This property that makes many of the thermoplastics particularly useful, i.e., low temperature deformation, also precludes the use of many thermoplastics in engineering applications where exposure to elevated temperatures is likely to be encountered. When relatively high temperature applications for thermoplastics are contemplated, it is often useful to employ a thermoplastic which incorporates, within the polymeric chain, one or more cyclic structures which typically raises the melting point or glass transition temperature of the polymer. Among the types of thermoplastics which incorporate a plurality of cyclic structures is the class known as polyarylate polymers. The polyarylates are typically esters of aromatic diacids and dihydric phenols. In such polymers, 2,2-di(4-hydroxyphenyl)propane, also known as bisphenol A or BPA, is frequently employed as the phenolic component. Nevertheless, glass transition temperatures at or above 200.degree. C. are not frequently encountered, in at least in commercial polyarylate thermoplastics. Moreover, certain of the thermoplastics which do melt or soften about 200.degree. C. are found to degrade upon conventional processing of the polymer. It would be of advantage to provide a novel class of thermoplastics of relatively high glass transition temperatures which are processable without undue degradation.